I didn't do detailed research, but it seems to me that the magnitude of Mellis' rumours depends on how much mad he is, so he must've been very, very angry himself.
To make up, it's the regular stuff - read books (of the ones You wish to be in good realtions with) and sacrifice stuff. Eventually, it will fix the relations... There is nothing as global good-rumours though... Collect orc, dark knight equipment on a level with the proper altar (polymorph another altar if necessary), and sacrifice it, again and again. It's tedious but with some effort, it should bring the good times back